Mass-capacity multimedia services and data gradually increase signal complexity and broaden a band in a wireless communication system. Correspondingly, a power amplifier which produces a final output in the system demands high efficiency and high linearity at the same time.
FIGS. 1A and 1B depict a conventional Radio Frequency (RF) power amplifier.
In FIG. 1A, I and Q signals generated at a baseband signal generator 100 are input to a baseband signal controller 102. The baseband signal controller 102 extracts an envelope of the signal. The envelope signal is supplied as power of a power amplifier 124 via a bias modulator 106. An RF modulator 104 modulates the baseband signal I+jQ received from the baseband signal controller 102 to an RF signal and outputs the RF signal to the power amplifier 124. The power amplifier 124 outputs a high-power RF signal by amplifying the RF signal.
The bias modulator 106 includes a linear amplifier 114 for supplying a linear current and a switching regulator 108 for supplying a high current. A control signal 150 of the switching regulator 108 is fed to a switch 118 via a Pulse Width Modulation (PWM) signal generator 110 that converts the envelope signal to a PWM signal and a switch driver 112 that regulates the signal magnitude to operate the switch.
The switching regulator 108 includes a power unit 116 for supplying the power, the switch 118 for switching on and off the power supply according to the control signal 150, an inductor 122 for removing a switching ripple of the current, and a diode 120 for building a current path when the switch is switched off.
In the bias modulator 106, the efficiency of the switching regulator 108 for supplying most of the currents is quite important. However, the switching regulator 108 is subject to a conduction loss caused when the current flows due to the resistance within the switch. That is the loss caused by the abnormal operation in the intrinsic loss of the component and the on/off state of the switch. That is a switching loss 156 superposed by the switching current 154 and the switch both-end voltage 152 as shown in FIG. 1B.